Drive unit for an electric hybrid vehicle

ABSTRACT

A drive unit for a hybrid electric motor vehicle includes a bevel pinion driveably connected to a power source, a bevel gear meshing with the bevel pinion and aligned with an axis, first and second drive shafts, a differential mechanism including an input secured to the bevel gear for transmitting power between the input and the first and the second drive shafts, an electric motor/generator including a rotor, and a planetary gear set driveably connected to the input and the rotor for transmitting power between the rotor and the input such that a speed of the rotor is greater than a speed of the input.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of and claims the benefit ofpending U.S. patent application Ser. No. 12/019,696 filed Jan. 25, 2008,which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a powertrain for a vehicle, and,more particularly, to a powertrain having multiple power sourcesincluding an electric motor for driving a set of vehicle wheels.

2. Description of the Prior Art

Hybrid electric powertrains have been developed that include an electricmotor and an internal combustion (IC) engine that can operateindependently or in combination depending on the driving conditions, thestate of charge of a traction battery, and the power source that mostefficiently meets the current power demands imposed by the vehicleoperator.

Most electric hybrid vehicles available commercially are front wheeldrive vehicles, in which only the front wheels are driven. Hybridelectric powertrains, being developed for use in four-wheel drivevehicles, allow both the motor and engine to transmit power to a rearset of driven wheels.

When packaging an electric motor drive unit for a rear axle it ispreferable to place the motor drive unit on the rear axle centerline forbest packaging efficiency. The engine is located at the front to thevehicle in the engine compartment. Such electric hybrid drive systems,however, present packaging difficulties to the vehicle designer,particularly when layshaft gearing is used to transmit power from alongitudinal drive shaft to a rear axle. A ring and pinion mechanicaldrive, similar to an axle drive, will operate without layshaft gearing.

A need exists for a low-cost, hybrid electric powertrain in which oneaxle is driven by an electric motor or an IC engine in combination withthe motor. To minimize cost, an electric machine would provide allhybrid functions including electric energy generation, electric vehiclelaunch, engine starting, electric boosting of engine power, andregenerative braking.

SUMMARY OF THE INVENTION

A drive unit for a hybrid electric motor vehicle includes a bevel piniondriveably connected to a power source, a bevel gear meshing with thebevel pinion and aligned with an axis, first and second drive shafts, adifferential mechanism including an input secured to the bevel gear fortransmitting power between the input and the first and the second driveshafts, an electric motor/generator including a rotor, and a planetarygear set driveably connected to the input and the rotor for transmittingpower between the rotor and the input such that a speed of the rotor isgreater than a speed of the input.

The ring and pinion mechanical drive, which is similar to an axle drive,allows the layshaft gearing to be removed.

A torque reaction member of the planetary gear set is secured to acasing against rotation, and a drum, which is secured to the gear,surrounds the planetary gear set. This arrangement minimizes the packagespace required to contain the drive unit.

The location of the drum and bevel gear facilitates their beingsupported on the casing for rotation. The layshaft gearing includes aminimum number of components.

The scope of applicability of the preferred embodiment will becomeapparent from the following detailed description, claims and drawings.It should be understood, that the description and specific examples,although indicating preferred embodiments of the invention, are given byway of illustration only. Various changes and modifications to thedescribed embodiments and examples will become apparent to those skilledin the art.

DESCRIPTION OF THE DRAWINGS

The invention will be more readily understood by reference to thefollowing description, taken with the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a powertrain for a hybrid electricvehicle, whose rear axle shafts are driven by an electric rear axledrive unit;

FIG. 2 is schematic diagram of the electric rear axle drive unit of FIG.1;

FIG. 3 is a schematic diagram of a second embodiment of the electricrear axle drive unit; and

FIG. 4 is a bottom cross sectional view of the electric rear axle driveunit shown in FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The powertrain 10 for a hybrid electric motor vehicle illustrated inFIG. 1 includes an IC engine 12, a transmission 14, which drives a frontfinal drive unit 16, driveably connected to a pair of front wheels 18,19 by front drive shafts 20, 21. Transmission 14 may be a manual gearboxor any type of automatic transmission. The front final drive unit 16also drives a rear drive take-off unit 22, which is connected to a rearfinal drive unit 24, i.e., the ERAD unit, by a longitudinal prop shaft26. The ERAD unit 24 is driveably connected to a pair of rear wheels 28,29 by rear drive shafts 30, 31. The ERAD unit 24 includes a casing 32,which contains the inboard ends of the rear drive shafts 30, 31.

FIG. 2 shows a motor/generator 34 arranged transversely in the finaldrive unit 24. The motor/generator 34 includes a hollow rotor 36, whichis connected by a sleeve shaft 38 to an input pinion 40 of a layshaftreduction gear train 42. Input gear 40 meshes with a large diameter gear44 secured to a layshaft 46, which also has a small diameter pinion 48secured to it. The small diameter pinion 48 meshes with a large diameterdriving gear 50, secured to an inter-wheel differential mechanism 53,which drives the rear wheels 28, 29 through drive shafts 30, 31. Driveshaft 31 extends concentrically through the rotor 36 and the sleeveshaft 38.

A coupler or clutch 52 alternately opens and closes a drive connectionbetween prop shaft 26 and input shaft 54, which is secured to a finaldrive bevel pinion 56. A bevel gear 58 meshes with bevel pinion 56 andis secured to the large diameter gear 44.

The motor/generator 34 is controlled by an electronic control unit (ECU)60. Electric power and rotating power are generated by themotor/generator 34 and by an integrated starter-generator 62, whichalternately drives and is driven by the engine 12. Both themotor/generator 34 and the integrated starter-generator 62 alternatelydraw electric current from and supply electric current to a tractionbattery 64 and an auxiliary battery 66. The traction battery 64 is ahigh voltage unit; the auxiliary battery 66 is a 12V unit for the supply& control of the vehicle electrical systems.

The engine 12 drives the front wheels 18, 19 through transmission 14,the front final drive unit 16 and the front drive shafts 20, 21, whilealso driving the rear wheels 28, 29 through the rear take-off unit 22,prop shaft 26, the ERAD unit 24 and the rear drive shafts 30, 31. Thetorque capacity of coupler 52 varies such that it transmits a magnitudeof torque to the rear wheels 28, 29 as required to maintain anappropriate torque split between the front and rear wheels. Under lowvehicle speed driving conditions, the electric motor/generator 34 drivesthe vehicle with the engine 12 stopped, in which case the coupler 52 isdisengaged and the rear wheels 28, 29 are driven only through thelayshaft reduction gear train 42.

When motor/generator 34 drives the rear wheels 28, 29, sleeve shaft 38transmits power from rotor 36 to pinion 40, which drives the largediameter gear 44, layshaft 46 and pinion 48. The input of differentialmechanism 53 is driven by large diameter driving gear 50. Under heavierload at low vehicle speed, the motor/generator 34 can supplement powerproduced by the engine 12.

At higher vehicle speed, engine 12 is the power source for driving thewheels, and the integrated starter generator 62 and the electric motorgenerator 34 supply electric power to the batteries 64, 66.

The layshaft reduction gear train 42 provides a reduction speed ratiobetween the motor/generator 34 and the differential 53 as well asproviding a reduction speed ratio between input shaft 54 and thedifferential 53. The layshaft reduction gear train 42, therefore,performs the dual task of providing speed reduction gearing for both theelectric motor/generator 34 and the mechanical torque path from theengine 12.

Casing 32 supports the various shafts and gear elements of the layshaftreduction gear train 42 and the stator 68 of the motor/generator 34. Thedrive shafts 30, 31 each comprise an inner shaft extending inside thecasing 32, an outer shaft outside the casing 32 extending towards arespective rear wheel 28, 29, and universal joints 70 connecting theinner and outer shafts and the respective wheel.

In the ERAD unit 24 illustrated in FIG. 3, bevel pinion 56 meshes with abevel gear 72, which is secured to a drum 74. Bearings 76, 78, fittedinto casing 32, support drum 74 in rotation about a lateral axis 84,which is concentric with shafts 30, 31. Drum 74 is driveably connectedto the input 86 of differential mechanism 53.

A speed reduction planetary gear unit 88 includes two interconnectedplanetary gear sets 90, 92. Gear set 90 includes sun gear 94; ring gear96; carrier 98, secured to differential input 86; and a set of planetpinions 100, supported for rotation on carrier 98 and meshing with ringgear 96 and sun gear 94. Gear set 92 includes a second sun gear 102;second ring gear 104; carrier 106; and a second set of planet pinions108, supported for rotation on carrier 106 and meshing with ring gear104 and sun gear 102. Ring gears 96, 104 are mutually connected by adrum 110, which is grounded on casing 32. Sun gear 94 is secured tocarrier 106 for rotation as a unit. Sun gear 102 is driveably connectedby a shaft 112 to the rotor 36 of motor/generator 34.

The angular velocity of sun gear 94 is about three times greater thanthat of carrier 98, and the angular velocity of sun gear 102 is aboutthree times greater than that of carrier 106. Therefore, shaft 112rotates about nine times faster than the speed of bevel gear 72, drum 74and differential input 86.

Differential 53 may be of the type comprising a ring gear that rotatesabout axis 84, a spindle driven by the ring gear and revolving aboutaxis 84, bevel pinions secured to the spindle for revolution therewithand for revolution about the axis of the spindle, and side bevel gearsmeshing with the bevel gears, each side bevel gear being secured to oneof the shafts 30, 31.

As FIG. 4 shows, the differential mechanism 53 may be a planetarydifferential mechanism 120, which includes a third sun gear 122driveably connected to drive shaft 30; third ring gear 124, secured bydifferential input 86 and drum 74 to bevel gear 72; third carrier 126,driveably connected to drive shaft 31; a third set of planet pinions128, supported for rotation on carrier 126 and meshing with sun gear122; and a fourth set of planet pinions 130, supported for rotation oncarrier 126 and meshing with ring gear 124 and the planet pinions 128.

A path for transmitting power from engine 12 to the rear axle drive unit24 includes transmission 14, rear drive take-off unit 22, and prop shaft26. A first power path within ERAD unit 24 transmits power from propshaft 26 through coupler 52, bevel pinion 56, bevel gear 72, drum 74 anddifferential mechanism 53, 120 to the rear axle shafts 30, 31 and rearwheels 28, 29.

When coupler 52 is open and the motor/generator 34 is operating as anelectric motor, a second power path within ERAD unit 24 transmits powerfrom the rotor 36 of the motor/generator 34 through shaft 112, gear set92, carrier 106, gear set 90, carrier 98 and differential mechanism 53,120 to the rear axle shafts 30, 31 and rear wheels 28, 29.

When coupler 52 is open and the motor/generator 34 is operating as anelectric generator, power from the rear wheels 28, 30 is transmitted ina reverse direction through the second power path to drive the rotor 36so that the motor/generator 34 can generate electric current.

The coupler 52 may be located in the front drive take-off unit 22instead of in the ERAD unit 24. The front drive take-off unit 22 mayincorporate a center differential, which continually splits the torquebetween the front wheels 18, 19 and the rear wheels 28, 29, in whichcase clutch 52 may be omitted.

Although the powertrain 10 has been described as having the engine 12 atthe vehicle front, the engine and transmission 14 may be located at therear of the vehicle or the engine may be located at the front andarranged along the longitudinal axis of the vehicle with a transmissionlocated behind the engine. References to “front” and “rear” in thisdescription are used primarily to describe the relative positions ofcomponents.

In accordance with the provisions of the patent statutes, the preferredembodiment has been described. However, it should be noted that thealternate embodiments can be practiced otherwise than as specificallyillustrated and described.

The invention claimed is:
 1. A drive unit for a hybrid electric motorvehicle comprising: a bevel pinion driveably connected to a powersource; a bevel gear meshing with the bevel pinion and aligned with anaxis; a first driveshaft and a second driveshaft; a differentialmechanism including an input secured to the bevel gear, for transmittingpower between the input and the first and the second drive shafts; anelectric motor/generator including a rotor; and a planetary gear setdriveably connected to the input and the rotor for transmitting powerbetween the rotor and the input such that a speed of the rotor isgreater than a speed of the input.
 2. The drive unit of claim 1 whereinthe planetary gear set further comprises: a first sun gear driveablyconnected to the rotor, a first ring gear held against rotation, a firstcarrier driveably connected to the input, and first planet pinionssupported for rotation on the first carrier and meshing with the firstsun gear and the first ring gear.
 3. The drive unit of claim 1 wherein:the planetary gear set further comprises a first sun gear driveablyconnected to the rotor, a first ring gear held against rotation, a firstcarrier, and first planet pinions supported for rotation on the firstcarrier and meshing with the first sun gear and the first ring gear; andthe gear unit further comprises a second the planetary gear set thatincludes a second sun gear driveably connected to the first carrier, asecond ring gear held against rotation, a second carrier driveablyconnected to the input, and second planet pinions supported for rotationon the second carrier and meshing with the second sun gear and thesecond ring gear.
 4. The drive unit of claim 1 wherein: themotor/generator further comprises a stator surrounding the rotor; theplanetary gear set includes a non-rotating member; and the drive unitfurther comprises a casing fixed against rotation, the stator andnon-rotating member being secured to the casing.
 5. The drive unit ofclaim 1 wherein the differential mechanism further comprises: a thirdsun gear driveably connected to the first drive shaft; a third ring geardriveably connected to the input; a third carrier driveably connected tothe second drive shaft; third planet pinions supported for rotation onthe third carrier and meshing with the third sun gear; and fourth planetpinions supported for rotation on the third carrier and meshing with thethird ring gear and the third planet pinions.
 6. The drive unit of claim1 wherein the differential mechanism and the planetary gear set aresubstantially aligned with the axis and the differential mechanism isspaced along the axis from the planetary gear set; the drive unitfurther comprising: a casing fixed against rotation; a first bearinglocated at a lateral side of the differential mechanism that is axiallyopposite the location of the planetary gear set, and supporting the gearunit on the casing for rotation about the axis; and a second bearinglocated at a lateral side of the differential gear set that is axiallyopposite the location of the differential mechanism, and supporting thegear unit on the casing for rotation about the axis.